A calanid copepod of the genus Calanus. In the North Atlantic, C. glacialis can be confused with congeners C. finmarchicus in the N. Atlantic and C. marshallae in the N. Pacific which both overlap in size and range with C. glacialis. Other species of Calanus overlapping in range with C. glacialis are C. hyperboreus, a significantly larger species and C. helgolandicus, a significantly smaller species.

5. the caudal ramus of C. marshallae is about twice as long as wide but less than the width of the anal segment whereas in C. glacialis and C. finmarchicus, the length is usually more than twice the width and about equal to the width of the anal segment. (Frost, 1974)

6. geographic distribution: C. marshallae has been identified only in the N. Pacific.

4. the geographical range of C. helgolandicus is centered in the eastern N. Atlantic and warmer waters of the western N. Atlantic while C. glacialis is primarily an Arctic species found in both the N. Atlantic and N. Pacific.